What causes ice to build up on an evaporator coil?

Ice buildup on an evaporator coil is primarily caused by low refrigerant levels. When the refrigerant level is insufficient, the evaporator coil does not receive enough refrigerant to absorb heat from the air passing over it. This results in the coil operating at a temperature that is too low, causing moisture in the air to freeze on the coil.

As the moisture freezes, it creates a layer of ice that further insulates the evaporator coil, leading to decreased efficiency and potentially causing the system to freeze up. Maintaining the correct refrigerant level is crucial for optimal system performance, as it ensures that heat exchange occurs efficiently and prevents ice buildup.